For producing a gas and/or oil field a hole is drilled into a number of geological formations. The gas and/or oil seeps through these layers into the hole from which the oil and/or gas is transported to the surface. For larger fields a main hole is drilled with a number of branches. To each branch oil and/or gas seeps and is collected into the main hole.
When producing an oil field or gas field it is desired to measure certain quantities in the wells. In for example a well with branches it is desired to detect if a branch still produces oil or gas or if for example water seeps into the branch. In this case the branch has to be shut off.
The applicant has developed sensors, which can be arranged into a hole in order to detect the certain quantities. These sensors are described in the international patent application WO 99/66172.
These sensors have to be arranged downhole at in some cases a few kilometres from the production platform. It is costly to provide cables downhole to the arrangement, which holds these sensors.